The present invention relates generally to fault isolation system of RF transmission systems, and more specifically to a mechanization which helps adjust the cathode voltage during an automatic fault isolation routine.
It has always been difficult to fault isolate failures between an electron tube RF amplifier and its high voltage power supply (H.V.P.S.). The main fault isolation difficulty between an electron tube RF amplifier and its high voltage power supply arises when the failure prevents turnon of the high voltage supply. Some of the more common reasons for this are: tube arc, improper cathode voltage, improper collector voltage, or a power supply failure. This assumes that all other tube voltages have been checked such as: filament voltage and current, grid bias, grid voltage and other anode voltages.
The task of correcting the voltage supplied to RF amplifiers in conjunction with fault isolation is alleviated, to some degree, by the prior art techniques of the following U.S. Patents, which are incorporated herein by reference:
U.S. Pat. No. 4,421,993 issued to M. D. Bloomer on Dec. 20, 1983; PA1 U.S. Pat. No. 4,247,801 issued to Dallos et al on Jan. 27, 1981; PA1 U.S. Pat. No. 4,090,106 issued to Okumura et al on May 16, 1978; PA1 U.S. Pat. No. 4,149,110 issued to Dallos on Apr. 10, 1979; and
U.S. Pat. No. 4,156,166 issued to Shapiro et al on May 22, 1979.
U.S. Pat. No. 4,421,993 discloses a load resistance control circuit which compares the actual value of a non-zero temperature coefficient load resistance to a desired load resistance magnitude. U.S. Pat. Nos. 4,247,801 and 4,149,110 each disclose a cathode current control system which includes an external circuit connected to the cathode and other electrodes of an electron discharge device for maintaining the electrodes at respective predetermined electrical potentials relative to the cathode.
U.S. Pat. No. 4,090,106 discloses a power supply circuit for an electron gun which automatically controls a voltage to be applied to a cathode so as to make an emission current constant. U.S. Pat. No. 4,156,166 discloses an electronics circuit for regulating the output flux generated by a lamp with the degeneration of the voltage from a power supply.
Conventional fault isolation systems normally bring power from the H.V.P.S. to the RF amplifier in a procedure which brings voltage all the way up in one step in a short time period. However, experience has shown that over 90% of the faults in the H.V.P.S. prevent even partial applications of voltage, while very few of the faults in the electron tube RF amplifier prevent at least a partial application of voltage.
From the foregoing discussion, it is apparent that there currently exists the need for a fault isolation system between a high voltage power supply and an electron tube RF amplifier that allows a partial application of voltage during a fault isolation test. The present invention is intended to satisfy that need.